This invention relates to fuel cells containing members comprised of carbon and, in particular, to techniques for inhibiting the corrosion of such members.
As is well known, fuel cells typically comprise an anode electrode for providing free positive ions upon exposure to a reactant fuel gas, an electrolyte for conveying these generated free ions and a cathode electrode for receiving the conveyed free ions in the presence of a reactant oxidant gas. In fuel cells of this type, strong acids such as, for example, phosphoric acid, are often employed as the ion carrying electrolyte. The anode and/or cathode electrodes, in turn, are often formed from carbon containing members, since carbon is compatible with the acid electrolyte environment. For example, carbon might be used to form an interior support for the catalyst in these electrodes.
It has been found, however, that even carbon containing members are susceptible to corrosion after long periods of time in the fuel cell environment. This corrosion is further aggravated when the fuel cell is operated at high temperatures and pressures (e.g., above about 375.degree. F. and in excess of about three atmospheres in a phosphoric acid cell) to achieve better performance. Higher fuel cell operating potentials (e.g., above about 0.8 volts in a phosphoric acid cell) also contribute to increased corrosion, these potentials being encountered when the fuel cell is operated at high temperatures and pressures to obtain high efficiencies and also at no load and partial load conditions. Finally, it has been established that this type of corrosion is more pronounced in the fuel cell oxidant gas cathode region.
To date a variety of techniques have been devised to counteract the above-discussed carbon corrosion in acid electrolyte fuel cells. These techniques have focussed on the carbon itself and have involved the development of different types of carbons such as, for example, synthesized carbons and glassy carbons, and the application of different heat treatments, such as different degrees of graphitization, to existing carbons.
It is an object of the present invention to provide a fuel cell having an improved resistance to carbon corrosion.
It is a further object of the present invention to provide a fuel cell having a gas environment suitably modified to realize improved carbon corrosion resistance.